A light emitting diode (LED) is a luminescence assembly. A luminescence principle thereof is to exert a forward bias voltage (current) on a III-V compound semiconductor material, and to utilize a form of combining electrons and electron holes in the LED with each other and converting energy into light, where light can be emitted during energy release and the LED will not be as hot as an incandescent lamp bulb after being used for a long time. The LED is advantageous in small size, long life, low drive voltage, high response rate and excellent seismic resistance, can meet demands for various lightweight, thin and miniaturized devices, and has become a product popularized in daily life.
Referring to FIG. 1 and FIG. 2, LEDs may be mainly divided into a vertical-type LED (FIG. 1) and a horizontal-type LED (FIG. 2) according to different drive structures (electrode structures). The LED structurally comprises a wafer substrate 1, an LED light-emitting layer 2 and a circuit layer 3, the wafer substrate 1 being divided into a conductive (vertical-type LED) substrate and a non-conductive (horizontal-type LED) substrate, and adopting a silicon substrate, a sapphire substrate, etc.
The LED light-emitting layer 2 comprises a first-type semiconductor layer 2a, a light-emitting layer 2b and a second-type semiconductor layer 2c, constituting a sandwich structure. The first-type semiconductor layer 2a may adopt an N-type semiconductor layer or a P-type semiconductor, and the second-type semiconductor layer 2c may adopt a P-type semiconductor layer or an N-type semiconductor correspondingly. The light-emitting layer 2b is made of a III-V compound material, which may be selected according to a wavelength to be emitted. The circuit layer 3 comprises a first-type electrode 3a and a second-type electrode 3b, which may be provided on the same side of the LED light-emitting layer 2 (horizontal-type LED) separately or two sides of the LED light-emitting layer 2 (vertical-type LED). Accordingly, after a voltage is exerted between the first-type electrode 3a and the second-type electrode 3b, an electron and an electron hole may be provided respectively, the electron and the electron hole may be combined inside the light-emitting layer 2b, and can further jump by steps to generate exciting light.
The current light-emitting performance and efficiency of the LED are increasingly advanced, a great variety of LEDs can be widely applied to daily life, an LED capable of emitting light having various colors such as red, orange, yellow, green, blue and purple as well as invisible light such as infrared light and ultraviolet light can be designed by utilizing the changes of various compound semiconductor materials and assembly structures, and various LEDs have been widely applied to outdoor advertising boards, stop lamps, traffic lights, displays, etc.
At present, LED chips are of a single light-emitting wavelength range specification, a packaging factory will package this chip of the single light-emitting wavelength range specification or needs to package two or more chips within different light-emitting wavelength ranges into an identical packaging body, the completed packaging bodies are arranged and assembled as required, a single chip or a single LED assembly is controlled by a control circuit, and LEDs having different light-emitting wavelengths generate mixed light to than a full-color display picture effect. But the prior art and structure will generate a large clearance between LEDs, thus being adverse to miniaturization.
Due to variation influences of manufacturing procedures and materials, main wavelength distributions of LED chips produced in each batch are different. When light having specific wavelength characteristics needs to be emitted, demands of light emission in different lighting occasions need to be met or a specific color for full-color display needs to be formed, in order to meet requirements for color accuracy, the earliest prior art refers to: binning many LED grains by utilizing spot measurement, sorting and binning programs to sort out LED grains close to the main wavelength distributions to result in considerable cost and time consumption of applications having different wavelength characteristic demands.
Therefore, an American patent filed U.S. Pat. No. 8,569,083 B2 discloses a structure having a plurality of light-emitting layers 22 over a substrate, a wavelength conversion convergence layer and a wavelength conversion layer are stacked in sequence, and light emitted by the plurality of light-emitting layers 22 is absorbed and converted through the wavelength conversion convergence layer and the wavelength conversion layer to make main wavelengths of finally-emitted light relatively consistent. Thus, a procedure of sorting and binning and then rearrangement according to main wavelength distribution in a known LED array grain manufacturing process is omitted, and production costs can be reduced.
However, repeated wavelength conversion results in that the utilization efficiency of light is low, the phenomenon of high heat is easily caused, miniaturization is difficult to achieve and high-brightness demands cannot be met. Moreover, a multi-layer stacking structure will increase manufacturing costs and reduce manufacturing yields, and demands in use are difficult to meet.